1. Field of the Invention
This invention pertains generally to high temperature kiln apparatus and more particularly to a safety door for utilization on rotary kilns of the type used in production of cement.
2. Description of the Background Art
Rotating cylindrical kilns are frequently used in the production of cement. The production of cement is a relatively complex process that involves mining and milling the raw materials which are then fed directly into a kiln or fed initially into a heat exchanger (typically a pre-heater or a pre-calciner) which discharges the material into a kiln and then fired to produce “clinkers.” The clinkers are subsequently milled and packaged for sale as cement. Such kilns operate at extremely high temperatures and, in some instances, include the injection of combustible waste materials as a source of supplemental heat. These kilns are lined with refractory brick which, in many cases, become coated with hard material during operation. The brick is a wear material that has to be replaced periodically. The brick and hard coating are removed by using a special piece of equipment that hammers the keyed brick out, allowing the material to fall into the bottom of the kiln. Most kilns have bolt on doors that must be removed in order to push the material out onto the ground or into a waiting dump truck. The doors are removed when positioned on top of the kiln and the kiln is then rotated so that the resulting opening or manhole is located on the bottom of the kiln. Once the material is loose and is lying at the bottom of the kiln, equipment is utilized to push the material which has fallen into the bottom of the kiln out through the open manhole.
Once the cleaning of the material lying on the bottom of the kiln has been completed, workers must enter the kiln to measure remaining brick thickness, measure replacement sections, or replace the retainer rings prior to installation of the new brick. During this time, the kiln remains in its rotated position wherein the open manhole is on the bottom portion of the kiln.
With the open manhole in such a position, a hazard is associated with workers entering and exiting the kiln during and after clean up because the open manhole is large enough for most workers to fall through. Most kilns are positioned such that they are on elevated support pedestals thus exposing a worker to a fall greater than the six foot fall allowed by protection equipment. In addition, wearing fall protection equipment inside a kiln is not practical because there are no areas on the internal surface of the kiln for the fall protection equipment to be secured to and because of the large number of people that may be required to be inside the kiln at any given time.
Covering the opening with a solid plate, grating or boards also exposes the worker to the same fall hazard. There is thus a need for a safety door which will automatically cover the opening and which will preclude workers from falling through the open manhole during the required maintenance of the internal surface of the kiln.